This invention relates to an apparatus for mixing and dispensing multiple-component substances, which comprises a housing for receiving at least two cartridges each containing a component, and a mixer head connected to the cartridges, a shaft for rotating a mixer element disposed in the mixer head, and pistons which are connected via a clutch to a drive motor for discharging the cartridges and which are adapted to be retracted at a speed higher than the advancing speed.
An apparatus of this type is known from German Offenlegungsschrift 3,723,517. There, the pistons for dispensing the cartridges are driven by the same motor as drives the shaft of the mixer element. The cartridges contain the component to be mixed, e.g. components of an adhesive which react chemically with each other and cure within a short time. When the cartridges are empty, the pistons are retracted by opposite rotation of the driving motor, whereupon the cartridges may be removed and replaced by fresh ones. While the known apparatus provides a high-speed retracting motion, the exchange of cartridges still requires rather time-consuming manipulation.
If it is intended to exchange the cartridges in a partly filled condition in order to use the same apparatus for mixing and dispensing a different substance, it is likewise required to retract the pistons by reverse rotation of the motor. After the new cartridges have been inserted, which may also be partly filled, the pistons are advanced by the regular slow movement, which take correspondingly long until they reach the contents of the cartridges. Further, as a result of this idle advancing movement, it will be difficult in practice exactly to meter the first partial amount of the new substance to be discharged.
European Patent Specification 0,057,465 discloses another apparatus for mixing and dispensing two-component substances in which the mixer head is detachable so that the same cartridges permit a plurality of individual quantities to be discharged with long interruptions in between. Prior to every new discharging step, the mixer head with the old mixture hardened therein is removed and replaced by a new mixer head.
In this device, the pistons are advanced within the cartridges by piston rods in the form of threaded spindles each of which is driven by a pinion carrier. When a cartridge is empty, one end of the piston rod will be at the foremost end of the cartridge, while the other end will project only slightly from the rear end of the pinion carrier. After a new, full cartridge has been inserted, the pinion carrier is reversed and replaced in such a manner that now the short end of the piston rod acts on the piston disposed in the cartridge. A time-consuming screwing-back of the piston rods is thus avoided.
Even in this device, however, there is the problem, that, when partially filled cartridges are exchanged, the piston rods will have to be rotated with respect to the pinion carriers either manually or by reversing the drive motor to bring them into engagement with the pistons inside the new cartridges. Unless this condition is exactly met, an idle advancing movement will occur when the apparatus is next operated, which results in an undesirable change of the relationship between the operating time and the amount of mixture being dispensed, possibly also of the mixing ratio between the two components.